1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to an apparatus and method for encoding Low Density Parity Check (LDPC) codes in a communication system.
2. Description of the Related Art
The next generation communication system is developed to support high-speed, high-capacity data transmission/reception for Mobile Stations (MSs). Particularly, in the next generation communication system, various schemes such as Hybrid Automatic Repeat reQuest (HARQ) and Adaptive Modulation and Coding (AMC) have been proposed for support of high-speed, high-capacity data transmission/reception, and the communication system should support various coding rates to use the HARQ and AMC schemes.
In addition, the next generation communication system considers using LDPC codes as well as turbo codes. LDPC codes are known to show high performance gain during high-speed data transmission, and can effectively correct errors caused by noises generated in a transmission channel, thereby contributing to an increase in reliability of data transmission. LDPC codes can be classified into Repeat Accumulate (RA) codes and Concatenated ZigZag (CZZ) codes. The RA codes are subclassified into regular RA codes and irregular RA codes, and the CZZ codes are subclassified into regular CZZ codes and irregular CZZ codes.
As described above, to use the HARQ and AMC schemes, the communication system should support various coding rates. There are various proposed schemes for supporting the various coding rates, and the typical one of the schemes is a puncturing scheme of supporting various coding rates using one catch-all codeword.
However, when the communication system using LDPC codes supports various coding rates using the puncturing scheme, an increase in puncturing rate causes degradation in performance of the LDPC codes. This is because the cycle structure on a Tanner graph of the LDPC code changes due to the use of the puncturing scheme. The term ‘cycle’ as used herein refers to a loop formed by edges connecting information nodes to check nodes in the Tanner graph of the LDPC code, and a length of the cycle is defined as the number of edges constituting the loop.
Therefore, there is a need for a Low Density Parity Check (LDPC) code encoding scheme for preventing performance degradation while using the puncturing scheme.